The need for certain vehicles such as heavy duty dump trucks, semi-trailers and the like, to have at least one (and often more than one) designated wheel bearing axle suspension system(s) capable of being raised and lowered selectively into and out of load bearing engagement with the road surface, is well-known in the art. This need usually arises in order that the vehicle be capable of legally satisfying maximum highway weight limit laws, as well as to provide an additional measure of safety when the vehicle is loaded. In this respect, such maximum weight limit laws often mandate, not just a maximum vehicle weight, but further prescribe (e.g., as by the so-called “bridge formula”) that the required number of axles needed be spaced in such a manner so as to distribute the weight of the vehicle and its cargo over a selected length of the vehicle. Such extra axles and their attached suspension systems are often referred to as “auxiliary” axle suspension systems.
The ability to lawfully carry the maximum weight of the load (cargo) allowed by law often translates economically into maximized profit and a more economically efficient use of the vehicle. However, it is also known that when the vehicle has one or more auxiliary axles added to its standard front and rear axles, three basic drawbacks arise when the wheels of the auxiliary axle(s) are in road engagement. The first is that cornering can become difficult. The second is that fuel efficiency can be reduced. Finally and third, is that tire wear can increase.
To overcome these drawbacks, the truck/trailer suspension art has designed and developed over the years numerous auxiliary axle suspension systems which are provided with a mechanism which when activated, usually from the cab of the truck or trailer, enables the wheels to be selectively raised out of or lower into load bearing engagement with the road surface, thus, mitigating (reducing) the above-described problems associated with auxiliary axle usage. Moreover, in those systems which are properly designed, when lowered into road engagement the suspension assumes its proper, safe and lawful share of the load. When not needed (e.g., when the truck is empty) properly designed suspensions can be activated to raise the wheels off the road surface a sufficient distance and maintain them at this distance from the road thereby to prevent inadvertent road contact, even when experiencing a curb or road bed irregularly. In this way, the system results in prolonged tire life and less fuel usage while making cornering easier when these “auxiliary” wheels can be lifted when cornering.
While numerous types of auxiliary lift axle suspension systems have been devised, only a relatively few types have been recognized as safe and effective for their intended purpose, and/or found over the years to be truly commercially acceptable. In this respect, the truly effective, safe and commercially acceptable designs are generally recognized as falling into three basic types of lift axle suspension configurations. They are: (1) the use of an inverted leaf spring as both the lift mechanism and as a longitudinal tracking beam, accompanied by an air bellows, deflated at lift position but when inflated against the leaf spring's upward bias, lowers the suspension into road engagement thereby achieving a full load bearing, air-ride characteristic (e.g., as disclosed in U.S. Pat. No. 3,285,621); (2) the use of a longitudinal, heavy, tracking beam and an opposing air-bellows arrangement at either end of the beam (as first pioneered in commercially successful form by Neway Corporation and later adopted by others); and (3) the use of various types of lift mechanisms in combination with a highly stable, weight reducing, parallelogram suspension configuration (perhaps one of the most successful of this type lift suspension to date being those embodiments as disclosed in U.S. Pat. No. 5,403,031).
Each of these three basic designs has its own distinctive features making it the choice of design of certain vehicle operators. Currently, however, most knowledgeable heavy duty truck and trailer operators recognize that for many commercial operations the characteristics resulting from the “parallelogram” type lift suspension result in the best performance, as compared to the other two types described above. For example, the parallelogram design is lighter in weight than the heavy duty beam type suspension, yet its parallel or only substantially parallel control arms located in approximately the same vertical plane, achieve a high degree of wheel “tracking” necessary for safety and acceptable tire life. Moreover, while parallelogram suspensions are generally heavier in weight than the automatic leaf spring lift-suspensions, the parallelogram design allows, in most instances, for much heavier loads to be safely, carried, while achieving at least equal “tracking” as the leaf spring lift design. Still further, the parallelogram design usually allows the suspension to have a shorter overall design length than either of the two other designs, enabling it to be placed on certain vehicles where the leaf spring lift and/or beam type suspension will not fit.
While the parallelogram type suspension is currently a rather popular design of choice due to its advantageous features as set forth above, when adopted to become a “lift” is axle, difficulties have historically been experienced in devising an acceptable lift mechanism that is able to efficiently and reliably, over an acceptable useful life, perform its intended task (lifting and lowering effectively, safely and lawfully). Thus, a need arose in the art for a lift axle suspension system of the parallelogram type, for both steerable and non-steerable suspensions, which had a truly effective lift mechanism that can achieve the basic characteristics of: lawful operation, effective lift, efficient lowering, and safe and effective suspension operation when in road engagement and long life of the various parts, including the lift mechanism.
This need was met, with high commercial success, by the unique, parallelogram lift axle suspension system as disclosed in the aforesaid U.S. Pat. No. 5,403,031 (with or without its unique axle caster adjusting feature). Moreover, in certain of the embodiment disclosed in this '031 patent, another problem attendant various former lift suspensions known as the “accordion effect,” (which shortened the life of the lift bellows), was overcome without the heretofore use of heavy, weight-adding, pivot bracketry. The '031 patent design achieved its improved results in this respect by a structure which enabled the lift bellows to expand and contract bi-directionally in a highly efficient manner, while achieving at the same time, as a parallelogram suspension, the known advantage of this type suspension. In addition, weight was reduced over the known heavy beam type suspensions and life expectancy of the lift bellows was increased due to the elimination of the “accordion effect” (a term used herein according to the meaning of that term in the aforesaid '031 patent). At the same time, efficient lifting was achieved in the embodiments of the invention disclosed in the '031 patent, while at the same time, the ability to carry more load in a lesser confined space than the known leaf spring lift design resulted. For the first known time then, the '031 patent disclosed a truly effective parallelogram type lift axle suspension system.
While advantageous, as well as being safe and effective for their intended purpose, the specific embodiments set forth in this '031 patent (as commercially exemplified by the Hendrickson Paralift™ and Paralift Ultra™ steerable and non-steerable lift axle suspension systems) were in need of further inventive improvement in order to meet certain particularly specialized applications in the art. For example, where, due to the large size and exceptionally heavy load carrying capacity of the vehicle on which the suspension was to be used, particularly high rigidity and strength of the suspension is required, whether the suspension is a steerable or non-steerable suspension, a need developed to achieve such high rigidity and strength without adding undue weight to the system. An example of such a need exists, for example, in the use of vehicles in mining of ore, in order to accommodate the exceptionally rough terrains often experienced in such operations.
In view of the above, it is apparent that despite the highly advantageous suspension designs disclosed in the aforesaid '031 patent, there remained a need in the art for a lift axle suspension, preferably of the parallelogram type, which incorporated the many unique and advantageous features of lift suspensions disclosed in the '031 patent, but at the same time provides a design of exceptional strength and rigidity, thereby to make it particularly useful in a wider variety of applications, steerable and non-steerable, including those uses where, due to the heavy duty nature of the vehicle and/or the environment of vehicle use (e.g., mining or other off-road operations) increased rigidity is required to assure appropriate high levels of safety and life expectancy of the suspension.
It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.